1. Field of the Invention
The present invention relates to image pickup apparatuses such as digital single-lens reflex cameras that use a battery as a power source.
2. Description of the Related Art
Battery residual capacity display devices for electronic image pickup apparatuses have been proposed. In some of such battery residual capacity display devices, a dummy resistor is connected between a battery and a circuit included in the battery residual capacity display device. A voltage is measured when a current is passed through the dummy resistor. A battery residual capacity corresponding to the measured voltage is displayed by referring to a camera storage value and a battery residual capacity display table.
Japanese Patent Laid-Open No. 2001-126778 discloses a battery residual capacity determination device having a subtable for each of a plurality of additional functions. The subtable details the correspondence between a battery temperature and a battery voltage drop. A battery voltage correction value is obtained on the basis of a battery temperature and a current battery residual capacity level. The obtained correction value is added to a measured battery voltage for battery voltage correction. This battery residual capacity determination device can improve the measurement accuracy of a battery residual capacity.
Examples of electronic image pickup apparatuses with battery replacement period display devices include a camera that stores in advance the number of times image capturing can be performed with a battery being used, adds up the number of times image capturing was performed with the battery, compares these values each time image capturing is performed, and displays a notification that the battery should be replaced when the difference between these values is equal to or smaller than a predetermined value.
Japanese Patent Publication No. 5-25102 discloses a camera that stores the number of times image capturing can be performed with a battery in a non-flash mode, represents the capacity of the battery as the product of N and the power consumption per single image capturing operation in the non-flash mode, and represents power consumption per single image capturing operation in a flash mode as the product of n and the power consumption per single image capturing operation in the non-flash mode. If the image capturing mode is the non-flash mode, a value representing the battery capacity is rewritten as N−1 each time the image capturing operation is performed and is then stored. If the image capturing mode is the flash mode, the value representing the battery capacity is rewritten as N−n each time the image capturing operation is performed and is then stored. Thus, this camera can display, in a plurality of image capturing modes, the number of times image capturing can be performed and the battery residual capacity.
In the case of the battery residual capacity determination method disclosed in Japanese Patent Laid-Open No. 2001-126778, current and power consumption at the time of image capturing are not taken into consideration when a battery voltage is measured. Accordingly, the power consumption of a battery cannot be measured and displayed. Furthermore, the number of images that can be captured with the battery, which represents the available power of the battery, cannot be determined and displayed.
In the case of the battery residual capacity determination method disclosed in Japanese Patent Publication No. 5-25102, the number of times image capturing can be performed with a battery is displayed in a plurality of image capturing modes. However, the integrated value of the current used for image capturing is not taken into consideration. Accordingly, if power consumption per single image capturing operation varies, for example, if an attached interchangeable lens is changed and power consumption required for an image capturing operation is therefore changed, the available power of the battery does not correspond to the displayed number of times image capturing can be performed with the battery. This decreases the accuracy of the counting of the number of images that can be captured.